Los Angeles: Serena Williams has reignited speculation that she could make a return to tennis, refusing to rule it out when asked and instead replying: "I don't know. But she re-entered the tennis anti-doping testing pool in December, setting off the rumour mill, only to deny that she was making a comeback. "No person that doesn't have intentions to play professional tennis is going to put themselves in that list, especially someone who has as much experience doing it as Serena Williams," Courier said. "Whether that's the mixed doubles at the US Open, whether that's doubles with her sister somewhere, whether it's singles, only she knows. The Williams sisters won 14 Grand Slam doubles titles as a pair and three Olympic gold medals.